The invention relates to optics for a bar code reader wand, and in particular to an improved mounting for a sapphire ball tip for a bar code reader wand.
Bar code readers are used to input information from bar code tags. Simply by scanning the bar code tag with a hand held wand, an operator can enter data for inventory control, process evaluation, point-of-sale pricing and various other operations. The scanned data may be processed by the bar code reader or relayed via a communications network to a remote host computer. A sapphire ball is often used in the tip of a bar code reader wand, because it provides a very smooth and hard surface that wears well and does not scratch the bar code tags. A sapphire ball also provides a good pivot point on which the wand can tilt for comfortable scanning.
There are, however, two main drawbacks to using a sapphire ball in the tip of the wand. First, the ball must be held firmly in place to prevent its falling out when the wand is dropped or hit on a surface. The mounting for the sapphire ball is a potential entry point for dust and other contaminants, and for electrostatic discharge (ESD) that could damage the sensor and circuitry inside the wand. Since bar code wands are often used in industrial applications where they receive rough handling, sturdy mounting of the sapphire ball in the tip is important.
Second, because sapphire has a high optical index of refraction (1.8) and the ball has a small diameter (on the order of 0.125 inch), the sapphire ball is a very powerful lens element. The effect of this optical element must either be incorporated into the optical train of the wand or it must somehow be neutralized. Incorporating the sapphire ball into the optical train generally requires that the ball be critically positioned with respect to other elements.
One example of a wand design that incorporates the sapphire ball into the optical train of the wand is shown in U.S. Pat. No. 3,784,794, "Electro-Optical Reader for Bar Codes or the Like", to Allais. Allais shows various embodiments in which the sapphire ball is used as a lens element both to focus light from a source in the wand for illuminating the bar code and to direct light reflected from the bar code to detectors in the wand. In several embodiments, the sapphire ball is simply held in a cylindrical passage at the tip of the housing of the wand. In another embodiment, the sapphire ball is mounted in a socket in a threaded aluminum support member.
In all embodiments, there is a fairly short path for leakage around the sapphire ball into the interior of the wand. Because of the optical constraints of incorporating the sapphire ball into the optical train, in all embodiments either the detectors or the light source are glued directly to the surface of the sapphire ball. This increases the susceptibility of the electronic components mounted on the ball to damage if dropped, makes assembly difficult to automate, and makes replacement of individual components of the tip impractical.
In another design known in the prior art and shown in FIG. 1, an optical flat 19 is ground on the sapphire ball 11 to eliminate the optical power of the back surface of the ball. The ball 11 is mounted in a housing 13 which also holds a sensor 15. In the design shown, the housing 13 is threaded so it can be screwed onto the tip of a wand. The ball must be secured, e.g., glued, in the housing in the proper orientation, with the optical flat 19 perpendicular to the optical centerline 17.
This design suffers from several disadvantages. It is expensive to grind the optical flat on the sapphire ball, and fixturing is required to properly orient the flat during assembly. The mounting provides a relatively short leakage path, and voids in the adhesive can result in leakage paths for dust and ESD.
It is an object of this invention to provide an improved mounting for a sapphire ball in the tip of a bar code reader wand that minimizes the effect of the sapphire ball as an optical element, securely holds the ball in place, and eliminates leakage paths around the sapphire ball for dust, ESD or other contaminants to the sensor and circuitry inside the wand.
These and other objects are provided by the mounting structure of the invention, a mounting nest for the sapphire ball having a hemispherical recess that contacts the surface of the sapphire ball to hold the ball securely, and molded from a material having a relatively high index of refraction so the optical effect of the surface of the all in contact with the recess component can be effectively neutralized.